<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <ul id="box">
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
    </ul>
    <script>
        var lis = document.getElementsByTagName('li')
            // for (var i = 0; i < lis.length; i++) {
            //     lis[i].onclick = function() {
            //         this.style.background = 'red'
            //     }
            // }
        var box = document.getElementById('box')
        box.onclick = function(e) {
            // console.log(event.target)
            e.target.style.background = 'red'
        }
    </script>
</body>

</html>